Tuesday, 8 January 2013

Implications for the Future

First of all I would like to thank you for taking the time to read this blog. I hope that you understand that there a numerous factors which could have been responsible for the extinction of megafauna during the Late Pleistocene. Overall, I have enjoyed conveying my thoughts and ideas on this widely disputed debate. I hope that (if you’re reading this) that you will formulate your own ideas on this matter, using the multitude of evidence available to come to your own conclusion. You never know, with improved fossil records your predictions might be proved right!

There are a few things that we can learn from the past, which can be applied to the present/future. The most important finding is that ecosystems are fragile things that are sensitive to both climatic and anthropogenic changes. It is important to recognise the pressures humans can cause to the environment, and seek to reduce these for the sake of future generations. Finally, It is important not to make the same mistakes as we did in the past, understanding the need to protect endangered species from possible causes of extinction.

Thanks for Reading 

It’s Here, The Conclusion you have all been waiting for…

It is now sadly time to come to a conclusion and unmask one of the biggest ‘whodunit’ mysteries. In this blog I will be stating the most important findings of this research, as well as delivering my own thoughts of what I believe to be the most likely cause of megafaunal extinction. The outcome of these blogs has revealed that climate and man are the two main culprits of extinction.

Man's Impact
The impact of man is one of the most popular reasons for the extinction of megafauna during the Late Pleistocene. Growing support for this theory is largely due to the arrival of Homo sapiens coinciding with the demise megafauna. This was found in many continents including Australia (Roberts’s et al 2001), North America and Eurasia. It is important to note that human overkill was not the same in each continent. Some regions may have experience blitzkrieg, whilst others might have shown evidence of protracted overkill. Increased number of Homo sapiens is a key factor which would have driven increased levels of hunting, and may have pushed megafauna to extinction. Numerous findings of sophisticated hunting technology such as spears, harpoons and nets (mostly used by Clovis hunters of North America) reinforce evidence to suggest that overkill was responsible for the decline of these great beasts. This is reinforced by Wong (2012) who states how changes in technology were responsible for the extinction of certain carnivores in East Africa. Bulte et al (2006) provides another theory, suggesting that hunting of mini-fauna would have increased chance encounters with megafauna leading to their eventual extinction. Looking at man’s influence in Australia, it was found that the extinction of 60 faunal species coincided with the arrival of humans 65,000 years ago (Jonson 2006). Evidence of butchered animals in Cuddie Springs (New South Wales) is an example which strengthens the overkill hypothesis. The extinction of animals resistant to glacial/interglacial cycles is another reason that portrays man as the culprit behind this controversial mystery. Hunting would have also selectively targeted larger animals, which provides an explanation of why only megafauna became extinct during the Late Pleistocene. The hunting of mega herbivores might have even caused the decline of carnivores that relied of these food sources (Wong 2012), illustrating the detrimental impact man can have on megafauna. The only continent that shows a co-existence between man and megafauna was Africa, and consequently this region experienced much fewer losses then other areas. The fire hypothesis has also shown to have a considerable effect of megafauna through extreme temperatures and landscape modification. The studies by Rick et al (2012) reveal that fire was of vital importance to humans as it was used for light, cooking, warmth, and allowed the creation of new technologies. Human induced fires were more common than lightning events, and therefore its effects can be linked to man’s impact on megafauna. Similarly studies in Tight Eastern Cave (South West Australia) found increasing charcoal concentrations coinciding with the arrival of Homo sapiens, suggesting that human induced fire was frequent. The impact of fire would have restructured plant communities causing vegetation to change. This might not have sustained megafauna and consequently led to their demise (Gill et al 2009). Overall, whilst it is clear that fire had some impact of megafaunal populations, it cannot be considered a key driver of extinction due to lack of evidence. We also looked at the likelihood of the occurrence of an extra-terrestrial event during the late Pleistocene (see Firestone et al 2007). Whilst the impact of a comet would have caused the extinction of megafauna, the lack of reproducible evidence (Haynes et al 2010) weakens this hypothesis. Man can be seen to be responsible for the death of megafauna through bringing hyper-disease (mostly carried by domesticated dogs). Megafauna had weak immune systems due to not being exposed to diseases. Their inability to withstand pathogens meant that hyper-disease is a mechanism of extinction. Rothschild and Laub (2006) reinforce this believe by showing the extinction of a particular type of mammoth through human carried tuberculosis. Evidence of this was found in the disease being present in 52% of the 118 skeletons that were surveyed. Whilst it is plausible in part, this theory lack much needed supporting evidence.

Whilst there are many reasons to suggest that man played a huge role in the extinction of megafauna, there is evidence which contradicts this. The lack of kill sites is a large factor that weakens the overkill hypothesis. Other evidence which disagrees includes the relationship between technology and hunting. Many believe that the improvement of technology was coupled with a varying diet as Homo sapiens had the newly found ability to obtain alternative food sources such as fish. Agriculture during the late Pleistocene may also reveal that man had access to an alternative food source, which would suggest that other factors might be responsible for the extinction of megafauna. Overall, poor quality fossil data sets make it exceptionally hard to determine whether primitive man caused megafaunal collapse.

There are many reasons why climate can be seen to be responsible for the collapse of megafauna. During the late Pleistocene climate was subject to large scale rapid oscillations between glacial and interglacial conditions. Such transitions would cause landscape modifications which in turn would have reduced the amount of suitable areas in which megafauna could survive. Climate changes would have also altered ecosystems and resulted in large vegetation changes due to the reduced growing season of plants. This would result in species with small ranges to subsequently die out. This is corroborated by Wroe (2006) and Dodson (1998) who found that Australia experienced an expansion of arid areas. Evidence which agrees with this hypothesis is also stated by Prescott et al (2012) who stated that the most rapid episodes of population decline were associated with the highest periods of temperature decrease. Such changes would have caused species such as the Eurasian musk ox and the woolly rhinoceros to become extinct (see Lorenzen et al 2011).
However, there is much evidence which disagrees with this hypothesis. The overall strength of the ‘man being responsible for extinction’ (mentioned above) severely weakens the climate hypothesis.

In my opinion I believe that the combination of both anthropogenic and climate forcing’s caused the extinction of the majority of megafauna. This belief can be strengthened because of the following reasons:
·         I believe that climate had the potential to exacerbate human impact. Glacial periods could have caused increased levels of hunting for survival.
·         Climate oscillations could have also been a significant factor in the evolution of tools specifically designed to hunt prey more efficiently. This resulting in increased numbers of megafauna being hunted and consequently led to increased extinctions.
·         The best example which incorporates both human and climate is the extinction of the woolly mammoth. Research by Nogues-Bravo et al (2008) found that suitable climate conditions for the mammoth reduced drastically between the Late Pleistocene and the Holocene resulting in 90% of its geographical range disappearing. Therefore climate would have significantly decreased the mammoth’s population size, and consequently would make them more vulnerable to extinction when hunting occurred.

Studies by Prescott et al (2012) and Prideaux et al (2007) found that the timing of megafaunal extinction is related to both climate and human forcing factors. Overall I believe Climate change could have weakened megafaunal populations, and with the combined presence of humans (which would have hunted, caused fires, and brought diseases) megafaunal extinction would have been inevitable. Hopefully with improved fossil records and data records the actual reason behind megafaunal extinction will be revealed.

Saturday, 5 January 2013

The Pro’s and Cons of the Sporormiella Proxy

 Sporormiella  spores used as a proxy to determine megafaunal existence

It has been argued that Sporormiella proxy can be used as a measure of large herbivore presence and abundance (Robinson et al 2005). In this blog I will explore the ideas of Feranec et al (2011), who looked at the advantages and disadvantages of using this proxy as an accurate dating method of extinct megafauna. An evaluation of this proxy might be useful in understanding whether it is a useful method of determining past megafauna during the Late Quaternary.

Proxies are widely employed in Quaternary paleoecology and the geosciences. When there is no direct method to establish organism presence, population size and other important demographics, proxies are used as a substitute (Feranec et al 2011). Sporormiella is a genus of fungi that is present on dung.  The spores are used as a proxy as they are preserved in lake sediments and easily identifiable due to being dark brown in colour and having a pronounced sigmoid germination pore.  Plant material and adhering spores are eaten by herbivores, and the spores pass through the digestive tract and are released as defecation. Spore abundance is related to the amount of dung present and has been an important tool in the analysis of extinct mammals in North America during the late Pleistocene.

Feranec et al (2011) identifies some of the problems with using Sporormiella as a proxy. Firstly, the fungus can be abundant on dung of the extant non-livestock megafauna and modern small mammals (Graf & Chmura 2006). This is problematic as it may weaken the accuracy of results looking at just solely megafauna. Secondly, a decrease in Sporormiella spore percentages does not necessarily mean a decline in megafaunal population size. Sporormiella is more abundant near lake shores than in the middle of lakes (Raper and Bush 2009), thus a decrease in this proxy could relate to an increase in lake level. Finally, Feranec et al (2011) raises concerns that the absence of Sporormiella does not necessarily mean an absence of large mammals from the local environment. An investigation carried out by Nyberg & Persson (2002) showed that habitat type had an effect in the abundance of fungi. This reinforces evidence to suggest that spore diversity is not necessarily related to megafunal presence or absence.

Therefore the issues associated with using Sporormiella as a proxy make it difficult to accurately determine megafaunal population presence, decline, and extinction during the late Pleistocene. To achieve robust interpretations about megafaunal extinctions and population collapse from Sporormiella counts, it is important to determine properties of the local vegetation and soil, as well as watershed characteristics and hydrodynamics of the study sites over time (Feranec et al 2011). Therefore it is important not to over rely on the accuracy of Sporormiella spores as other proxies provide better understanding for end-Pleistocene extinction. The use of Sporormiella should not be disregarded complexly as it is a potentially promising, and analysis in later years might become a more accurate method of dating. Using Sporormiella with other proxies would provide a most accurate and reliable technique of determining presence and abundance of megafauna as well as reasons behind population extinction.

Thursday, 3 January 2013

Unravelling the Mystery Behind the Extinction of the Woolly Mammoth

In past blogs we have looked at the various different factors that could have potentially caused the extinction of megafauna during the Late Quaternary. We have also looked at some examples of megafauna that became extinct, as well as looking at reasons behind extinction patterns in the continents of Africa and Australia. We are sadly almost coming to an end of ‘The Might of Megafauna Reasons for Mass Extinction’, however in this blog I will like to explore the mystery behind the extinction of one of the most renown megafauna; the woolly mammoth.

Mammoths are common mammals
 in popular film. Examples include;
Manny in Ice Age
If you ask anyone to name a species of extinct megafauna they generally say ‘the woolly mammoth’.  In fact, the mammoth is frequently shown on popular films such as Ice Age or 10,000 BC, which both show the various natural and anthropogenic forcing factors that could have driven its extinction. The woolly mammoth (Mammuthus primigenius) was a herbivorous mammal that inhabited  the open steppe-tundra’s of Eurasia and North America from late Middle Pleistocene 300 ky BP. The species survived through different climatic cycles until they vanished during the Holocene around3.6 kr BP (Nogues-Bravo et al 2008). If you look at my previous blog; 'Some examples of extinct megafauna in relation to climate and human impacts', it is apparent that the causes of extinction for the woolly mammoth are unclear. The last area in which they inhabited was Wrangel Island in Arctic Siberia, and the most likely explanation for their disappearance has mostly focused on climatic and anthropogenic forcing mechanisms. Both these mechanisms alone are credible causes of extinction (as we have seen in past blogs), but a combination of climatic changes and increased human pressures might provide a better explanation of the extinction of this species.

Could a combination of Climate and Man be responsible
for the extinction of the mammoth?
The proposal that climate was responsible for the extinction of the woolly mammoth is reinforced by Nogues-Bravo et al (2008) who found that suitable climate conditions for the mammoth reduced drastically between the Late Pleistocene and the Holocene resulting in 90% of it is geographical range disappearing between 42 ky BP and 6 ky BP. Such climatic extremes would have caused a significant decrease in the mammoth’s population size, and consequently would have made them more vulnerable to extinction when hunting occurred. There is also a correlation between the reduction of climatically suitable areas, an increase in anthropogenic activities (probably driven by increased population densities) and the gradual disappearance of the woolly mammoth. Many people believe that the warming of the climate during the Holocene was responsible for the demise of these great beasts, for example Ugan & Byers (2007) completely disregard the overkill hypothesis, believing that large climatic shifts would have caused the mammoth to die out. However, evidence shows that mammoths had previously survived period of warming, which suggests that a combination of climate and anthropogenic impacts might be more plausible mechanisms of extinction. Climatic warming resulted in mammoths moving to less hostile areas such as Arctic Siberia (where the latest recordings of mammoths have been found), which suggests that other factors must have contributed to the complete extinction of this species. Climatic oscillations are highly important to this debate as they would have modified the landscape and reduced the geographic range in which mammoths could survive.

I found this useful map in Nogues-Bravo et al 2008 showing the projected climatic suitability for the woolly mammoths Pleistocene and Holocene. The red areas indicate the climatic areas of suitability for mammoths. Black dots are records of mammoth presence. Black lines represent the northern limit of modern humans. 
The proposal that man played a significant part in the extinction of the mammoth are shown where human populations started dispersing across northern Eurasia around 40 ky BP (Nogues-Bravo et al 2008). Research carried out by Nogues-Bravo et al (2008) led to the creation of a model which combined changing climatic conditions and the intensification of human hunting using fossil records and climate simulations. Results from this investigation show that altering climate conditions was responsible for; reducing the distributional range of the mammoth, a decrease in the species population size, and ultimately an increase in the risk of extinction. When climate is combined with the intensification of hunting, the extinction of the woolly mammoth was inevitable. Nogues-Bravo et al also reveals that one woolly mammoth killed every three years by each human being in-habiting its distribution range would be sufficient to lead the species to extinction (2008). Similarly Haynes (2003) states that even low levels of hunting could eradicate a whole mammoth population. Therefore, human hunting alone had the potential to be solely possible for the extinction of the species; however there is lack of evidence (in the form of kill sites) which supports this belief.  Conversely, in the absence of human hunting, mammoths might have been able to survive in refuge spots (small climatically suitable areas) thus environmental change alone appears insufficient to account for such extinction patterns (Stuart 2005). Consequently the most widely held belief is that the synergy between the collapse of suitable climatic conditions combined with the northward increase in human population densities set the place and time of the mammoths extinction (Nogues-Bravo 2008). The likelihood of humans causing extinction of mammoths  through introducing new pathogens (hyper disease theory )is highlighted by Rothschild & Laub in 2006 (see hyper disease blog) . In this investigation, it was shown that the extinction of a particular type of mammoth was caused by human carried tuberculosis and found in 52% of the 118 skeletons surveyed. However, this theory lacks much needed evidence to support it, including proof of a disease that has the capabilities to wipe out an entire species.

As mentioned above, the youngest remains of woolly mammoths are found on Wrangel Island (7,000-4,000 yr BP). This example shows how mammoths managed to survive climatic changes largely due to the separation of the island around 12,000 BP which consequently altered local topography and climatic features, which permitted relictual preservation of communities of steppe plants (Vartanyan et al 1993). With this example, it is interesting to note that skeletal remains on the island were of dwarf mammoths probably because of the insularity effect, combined with a response to the general trend toward unfavourable environment during the Holocene (Vartanyan et al 1993). Research has shown that other areas e.g. Mongolia, might have been of suitable climatic conditions for mammoths to survive. No records of mammoth remains have been found in these regions, suggesting that mammoths remained in High Arctic Siberia (small geographic distribution), which would have challenged the survival of the species when faced with human hunting pressures.  It is also possible that climate might exacerbate human impacts (Wroe et al 2006), resulting in increased levels of hunting for survival.

Skeletal remains of a dwarf Mammoth found on Wrangel
In conclusion, a definite cause of extinction of the woolly mammoth has yet to be determined and will continue to be subject of debate for a very long time. Many believe the influence of climate was responsible for extinction, causing colder winters, warmer summers and drier conditions (Oard 2000), however the survival of mammoths into the Holocene as well as the adaptability (dwarfing) shown on Wrangle Island shows that this extinction process is complex. Glen MacDonald of the University of California (Nature Communications) stated that ‘findings dispel the idea of any one factor, any one event, as dooming the mammoths’. This reinforces evidence to suggest a multitude of factors can be linked to the demise of the mammoths. Overall, I strongly believe that habitat change (caused by shifting climate) would have decreased the population of the species and would have driven mammoths to areas such as Arctic Siberia. This, combined with human pressures (hunting practices) provides a strong explanation for the extinction of the woolly mammoth.

The link below gives a great overview of the mammoth mystery:

Remains of a mummified baby woolly mammoth named Lubya

Wednesday, 2 January 2013

Reviewing the Theory that; ‘Humans 2 Million years ago Doomed Large Carnivores’

Some of the carnivores species to become extinct
 include the saber toothed cat.
So far we have uncovered that there is a huge difficulty in deciding which mechanism was responsible for the extinction of megafauna during the late Pleistocene. An article by Kate Wong (2012) was recently given to me, and in this blog, I will review her ideas as they are highly relevant to the megafaunal debate.

The article immediately determines that humans were not only responsible for recent environmental changes (Anthropocene), but also the extinction of certain carnivores in East Africa, largely due to shifts in technology and diet (Wong 2012). This belief is highly credible as in past blogs we have already seen the impact of sophisticated hunting technology used by Clovis hunters of North America, which may have caused megafaunal extinction on this continent. Therefore, the progression and transformation of basic hunting sticks to stone spears, harpoons and traps suggests that Homo Sapiens had the technology available to kill carnivores.  Alternatively, as human populations grew, it may have caused increased levels of hunting in order to provide enough food to sustain the population. Species that would have been targeted include mega herbivores, and there dramatic decrease in numbers may have caused habitat modifications as well as the decline of carnivores that relied on these food sources. Carnivores that would have suffered include; saber toothed cats, bear sized otters and omnivorous bears. All of these species began dropping precipitously around two million year ago (Wong 2012).

Could more sophisticated technology cause the extinction of Carnivores?
Wong (2012) highlights that climate could not have been the culprit as small carnivores did not become extinct. This is controversial as smaller mammals may have been more resilient to climatic changes and able to find refuge spots enabling their survival. As well as this, climate change would have caused large scale habitat modifications, altering ecosystems. Such changes would have drastically affected larger species that require large amounts of food to survive. This is reinforced by Owen Smith who stated that such habitat changes (as a result of climate change) would have been detrimental to the distribution and abundance of herbivores (1987), which would have affected carnivore populations.

Could climate have caused extinction through habitat modification?
Wong (2012) states that human omnivorous diets may have even caused humans to hunt carnivores for meat; however this theory, in my opinion, is unlikely to have caused the death of all mega carnivores. Other theories are much more realistic causes of extinctions, having more evidence to support them. Lar Werdelin (of the Natural History Museum in Stockholm) states that humans drove carnivores away from kills during scavenging, and this is reinforced by Oakley (1961) who stated that it has been reported that African children have been known to drive lions from their kill. However, whilst this may have occurred, the likelihood of the majority of East African mega carnivores being extinct due to this reason is doubtful.
Humans chasing away scavenging lions. Could starvation
 be the cause of extinction?
 Further evidence with disagrees with the influence of human overkill include the advancement of agriculture which would have provided an alternative food source and consequently reduced hunting practices. Wong (2012) also states of a correlation between the timing of the decline of species and the arrival and expansion of humans. Whilst this may be so, this could be a mere coincidence. Alternately humans may have also caused the arrival of disease (from non-native species) as well as increased fire regimes, both of which have the influence to drastically reduce megafaunal numbers. Consequently the cause of extinction patterns still remains unclear.
Could increased fire regimes be responsible for the extinction of carnivores?
In conclusion, the theory’s put forward by Wong (2012) are intriguing to this debate. Whilst there are many theory’s that can be put forward to explain the decline of East African carnivores, actual reasons for such extinction patterns remain unclear. Whilst the overkill theory has gained much support over the years, there is still an urgent need for improved fossil resolution that would capture more details of past events. Overall I personally have to disagree with the beliefs put forward in Wong’s (2012) argument. I believe that human hunting was a highly influential mechanism in causing some extinction of African carnivores, but I believe that the arrival of humans would have been coupled with the increased fire regimes, as well as disease, which would have contributed to such extinctions. Similarly the combination of human and climate forcing’s providing a stronger  explanation for such large extinction patterns.